This invention relates generally to central tire inflation systems (CTI Systems or CTIS) and, more particularly, to a method for achieving more accurate higher tire pressure measurements in a CTI system by ensuring sufficient wet tank pressure prior to initiating a tire pressure check sequence.
Central tire inflation systems are well known as may be seen by reference to U.S. Pat. Nos. 640,331; 4,678,017; 4,754,792; 4,782,879; 4,804,027; 4,883,106; 4,898,216; 4,922,946; 4,924,926; 5,174,839; 5,253,687; 5,180,456, the disclosures of which are incorporated herein by reference. Each of these systems allow a vehicle operator to remotely vary the air pressure in vehicle tires to dynamically alter the tractive ability of the tires depending upon the terrain and the load carried by the vehicle.
In order to accomplish this, a system controller calculates an optimum tire pressure for the current conditions under which the vehicle is operating, or otherwise receives a desired pressure directly from the vehicle operator. The controller attains the programmed tire pressure by issuing command signals to electronically controlled pneumatic components of the system which cooperate to inflate or deflate the tires as required. To achieve and/or maintain the desired tire pressure, the CTIS controller initiates a tire pressure check at vehicle start-up, periodically during vehicle operation and at various points in the inflate or deflate sequences. If the pressure check indicates that the current pressure is greater or less than the desired pressure, a deflate or inflate sequence is initiated.
However, in performing the tire pressure check sequence, it is assumed that pressure in the supply air reservoir, or wet tank, is greater than tire pressure. Due to the manner in which tire pressures are measured in the type of system described herein, a wet tank pressure below tire pressure will result in an incorrect measurement wherein tire pressure is misread as the lower wet tank pressure. Although wet tank pressure is usually sufficient, primarily due to a pressure switch which ensures at least a minimum wet tank pressure before the CTIS is allowed to consume any air, the ever increasing operating pressures of tires today are beginning to exceed this minimum pressure. This could lead to a situation where a measurement is taken when tire pressure is greater than wet tank pressure, thereby resulting in one or more improper inflate sequences which must subsequently be reversed by corresponding deflate sequences once a correct tire pressure measurement is obtained.
Current methods which assume an adequate wet tank pressure thus allow inaccurate tire pressure measurements when the wet tank or supply air pressure is lower than tire pressure. Guarding against this occurrence has required setting a maximum tire pressure which is lower than the minimum pressure switch setting and thus lower than necessary or even lower than recommended for a given condition and vehicle load. Therefore, there exists the need to ensure accurate higher tire pressure readings by making sure wet tank pressure is above tire pressure when the tire pressure reading is taken.